The present invention is with respect to a union for medical instruments or pipes such as catheters, probes and flexible piping generally, more specially for injection, transfusion or infusion. In fact, while the present invention is more specially directed to a union for pipes, it is to be kept in mind that its teachings may generally be used in the design of fastener-like unions without any fluid connection function. The sort of union on which the present invention is more specially based is one having a male half with a solid or hollow spigot of generally round cross-section and having at least one radial nosepiece on its outer face. The union of the invention is furthermore made up of a female part with a middle axis socket for taking up the spigot of the male half, the socket having at least one locking nosepiece in the path of motion of the radial nosepiece on the spigot when the spigot is moved into the socket. Furthermore, the locking nosepiece of the female half is such as only to let the spigot be pushed home into the socket when elastic deformation takes place, that side of the locking nosepiece which is to the back (as seen in the direction of motion of the spigot when moved into position) having a stop face for acting against a back stop, the word "back" again being used in connection with the direction of motion of the spigot into the socket, for acting on such radial nosepiece and locking it into place. The invention is furthermore directed to the female half of the union as such.
The most common make of union or coupling on these lines used in the field is the Luer or Record union, which generally has, on the one half, a union nut, which may be separate or fixed to an instrument, with generally a double-start thread with a helix angle of 12.degree. and within this thread there is a coned pin part with a duct running therethrough. The male half of the union is in the form of a coned spigot with an inner face or bore having the same cone angle, and in the joined-up condition of the union the male half is slipped on the outer coned face of the pin part so as to be rested fluid-tightly against it, that is to say when the male half has its circumferential wall in the space between the thread and the coned pin part. On its outer face the male half has nosepieces, like small lengths or pieces of a screwthread, which are screwed into the two-start female thread of the union nut so that, on turning the female and male halves in relation to each other, such nosepieces will be screwed into the female thread till the pin part is moved right home into the coned spigot or sleeve. However, it is not necessary for all unions to have the mating faces on the pin part and the spigot or sleeve in the form of a cone and in fact only one of the two faces may have a coned form so that there will only be contact along a line between the two parts, such line contact nevertheless giving a full sealing effect. Furthermore, it is possible for the union nut to be joined to a cylindrical stem while the male half is in the form of a cylindrical spigot if the one part is fixed, after being moved right home, in relation to the other by radial stops for example, or if the union is not to be fluid-tight. For doing up the union, the male half with the nosepieces thereon is placed against the female thread of the female half and then the male half is screwed into the female half until, because of the slipping motion of the spigot of the male half in an axial direction in relation to and on the pin of the female half, the union has been done up to the desired degree. In the case of a union with coned sealing faces there will be a high enough degree of static friction between the coned faces forced against each other to keep the parts of the union fixed together. The union nut in addition keeps the two halves fixed together because the nosepieces are screwed into the thread of the union nut. For this reason, the union may not be separated into its two halves when acted upon by a strong pulling or bending force.
More specially in unions in which the male and female halves are made of synthetic resin or plastic, which may be desired for reasons of price because such unions are generally not used more than once, a self-locking effect will be produced in the fully done-up position of the union nut on the thread even although the helix angle of the threads is great, such self-locking effect being caused because of the screwed up threads parts being elastically bent to some degree and, for this reason, locked at such points by static friction; however, this condition may only be produced on using a certain amount of force for doing up the union nut. If, however, the union nut is not done up tightly enough (if the patient makes an attempt at turning the union nut or if the union nut becomes loose and turned out of its fully done-up position for some other reason, the union nut will no longer be locked and tightly done up in position, even in this case of a synthetic resin structure. Such loosening of the union nut may be caused by a small angle of turn, which is unlikely to be seen on examination of the union by eye. However, even in such a condition, in which the union nut has only been unscrewed to a small degree, there will no longer be a positive and full locking effect between the male and female halves, the two only being kept done up by static friction, if in fact the sealing faces are coned or flared. If then the union is acted upon by a pulling or bending force, as will frequently be likely if the union is carelessly handled, the static friction effect will be overcome and in fact it is likely for the male half to come completely out of the female half. The outcome of this will, clearly, be serious and may even be the cause of the death of the patient. If the union nut is made in one piece with the rest of the female half, the female and male parts will have to be turned in relation to each other for doing up the union, the nosepieces on the male half having to be screwed into the female thread of the union nut. These nosepieces are placed at the distal end of the male half (that is to say at its end furthest from the apparatus to which it is joined) so as to make certain that the nosepieces are taken up in the female thread once the male half has only been slipped a small distance into the union nut and overlapped thereby.
One sort of prior art union on these lines is to be seen in German Offenlegungsschrift specification 2,657,215, the union being designed as a quick-release coupling. Its female half has two oppositely placed locking nosepieces at its distal end (that is to say its end furthest from the apparatus with which it is joined), while on the other hand the male half has at its proximal end (the end nearest the apparatus with which it is joined and to the back in the direction in which the male half is moved into the female half doing up the union) a ring-like shoulder around it as a nosepiece or catch. For doing up the union, the front, uncovered spigot of the male half is pushed into the female half so that the spigot is taken up in a coupler of the proximal end of the female half. The male half is slipped in until its proximal nosepiece has been moved past the distal locking nosepieces (with elastic deformation) on the female half and has snapped in or detented in on the proximal side thereof. For making certain that the union may be quickly undone, the distal part of the female half (that is to say the part furthest from the apparatus with which it is joined) may be bent elastically by the user's fingers so that the two diametrally opposite locking nosepieces are moved further away from each other, freeing the ring-like nosepiece on the male half.
Although this prior art union has the useful property of being able to be undone very quickly, this is at the price of its not being completely safe, inasfar as the female half may be bent in error so that the male half will no longer be kept in position. Furthermore, the material of the female half has to be soft in its properties so that it is bent to the desired degree simply by pushing against it with one's fingers. Because of this, the front or distal part of the female half may not be so designed as to give any help in keeping the spigot locked in position. In fact, if pulled upon, the spigot may be pulled clear of the female half and furthermore, if the union is acted upon by a bending force, the proximal locking nosepiece of the female half will be bent because of this so that leaking is likely when the union is acted upon by bending forces and, in fact, the union may be completely separated. In any case, if pulled upon and bent at the same time, the connection will very quickly be broken.
Furthermore, the union of the said German specification 2,657,215 is made with specially matching female and male halves, which may not be used with other makes of unions. In fact, the male half may in no case be used with a screwunion part, as for example part of a Luer-Lok union and if the male half is to be joined up with some other part of the apparatus, it is necessary for all such parts to have female halves of matching design. However, it is frequently the case that a union has to have different properties to be in line with the function of the connection made therewith at any given time; to take an example, a quick-connection-function may be needed which does not have to be very safe while in an other case the connection produced has to be completely safe, that is to say more or less impossible to undo because of some undesired effect. Lastly, many forms of apparatus have connection parts, as for example female halves of standard unions such as Luer unions, and have to be changed in design if they are to be used with a spigot of the union of the said German patent specification 2,657,215; such changes in the design or even the use of a special adapter piece having one end matching the union of German specification 2,657,215 and the other end matching a Luer union, are naturally complex.